The present invention relates to ovens for preparing food and in particular to an oven that can provide for more accurate temperature monitoring and temperature control.
High-end commercial ovens may provide for multiple cooking modes including heat augmented with forced airflow (convection) and heat augmented with steam. Generally, convection cooking uses a fan to disrupt the insulating effect of stagnant air around the food, increasing the heat flow to the food. This increased heat flow may be used, for example, to promote surface browning of the food. In contrast, the application of steam (typically also with operation of the convection fan but may also inject steam directly onto a heating element without operation of the convection fan) can provide for fast cooking while retaining food moisture, flavors, and nutrients. Steam cooking generally prevents surface browning. These different modes may be combined in sequence during a cooking cycle, for example, to rapidly cook meat and then to brown its surface. Commercial ovens may also provide “cook and hold” modes including heat surrounded cavities without the use of convection fans, forced air, or application of steam to allow even cooking with greater moisture.
Different heat sources are commonly used for ovens including electrical heating elements, which employ electrical current passing through a resistance in communication with the oven cavity, and gas heating elements, which provide for the combustion of gas and the circulation of the combustion exhaust through a heat exchanger in communication with the oven cavity. Temperature control of the oven is typically provided by switching the electrical current or the gas on and off according to a sensed temperature of the oven cavity. Such switching between on and off states greatly simplifies the control of the electrical current and gas elements.
Ovens of this type are commercially available from Alto-Shaam, Inc. of Menomonee Falls, Wis., and are described generally in U.S. Pat. No. 6,188,045, entitled “Combination Oven with Three Stage Water Atomizer” hereby incorporated by reference.
Ovens normally operate according to a feedback control system in which a desired oven temperature is compared against an actual measure of the oven cavity temperature and the difference used to control the heating element. The oven cavity temperature is normally measured by an electronic temperature sensor such as a resistive temperature detector (RTD), thermocouple, or solid-state temperature sensor. The desired oven temperature (also termed the set point temperature) can be entered by the user through a panel control or the like.
Often the temperature measured by the electronic temperature sensor may fail to accurately reflect the cooking temperature of the food in the oven. This can be because of temperature stratification (for example, caused by convection) where the temperature sensor senses an extreme in temperature that is not representative of the general oven temperature, radiant energy absorption by the sensor directly or reflected from the walls of the oven, temperature “shadowing” by a product placed near the location of the sensor that cools the air around the sensor, water or moisture on the sensors causing poor sensing, and “dead zones” in which the temperature sensor is located in an air pocket that is isolated from other oven air, for example, by food tightly packed on the racks or as a result of persistent airflow patterns.